1. Field of the Invention
The invention relates to a brake control apparatus and method that controls braking forces applied to wheels of a vehicle.
2. Background of the Invention
Japanese Patent Application Publication No. 2006-123889 (JP-A-2006-123889) describes a hydraulic brake system including a hydraulic pressure booster, a master cylinder, a power hydraulic pressure source and multiple brake cylinders. In this hydraulic brake system, the multiple brake cylinders may be selectively communicated with the hydraulic pressure booster, the master cylinder and the power hydraulic pressure source using a simple circuit. This structure provides greater control over a hydraulic pressure. If the brake system is operating normally, hydraulic fluid is supplied from the power hydraulic pressure source to the brake cylinders. If a malfunction is detected, the brake system control mode is changed from the normal control mode to a different control mode. For example, the hydraulic brake system control mode may be changed to a control mode in which the hydraulic brake system is divided into two systems. In one of the two systems, the hydraulic fluid is supplied from the master cylinder to some wheel cylinders. In the other system, the hydraulic fluid is supplied from the hydraulic pressure booster to the remaining wheel cylinders.
However, if the detected malfunction is leakage of the hydraulic fluid, and the malfunction occurs in a fluid supply path through which the hydraulic fluid is supplied from the hydraulic pressure booster to the wheel cylinders, the hydraulic fluid supplied from the hydraulic pressure booster is wastefully consumed to the leakage. The original function of the hydraulic pressure booster is to amplify the brake operating force by several times or several tens of times and output the amplified the brake operating force to the master cylinder, thereby reducing the effort that a driver need to expend to operate the brake. However, if the hydraulic fluid from the hydraulic pressure booster, more specifically, the hydraulic fluid from a high-pressure accumulator which causes the hydraulic pressure booster to generate a hydraulic pressure, is wastefully consumed, the above-mentioned function of the hydraulic pressure booster is no longer attainable. In this case, the function of the hydraulic pressure booster deteriorates, and, in addition, the brake pedal undergoes so-called “kickback”. As a result, the operability of the brake pedal or the brake feel changes.